Vertical cavity surface emitting semiconductor laser based on lateral epitaxy technology and preparation method thereof

Abstract

The application discloses a vertical cavity surface emitting semiconductor laser based on a lateral epitaxial technology and a preparation method. The core of the structure is to solve the problem of presetting a lower DBR through the lateral epitaxial technology, to preset the DBR first, to open a window on the DBR, to grow the functional area of the laser on the upper side of the DBR through the lateral epitaxial technology, to complete the preparation of the lower DBR, and then to prepare the upper DBR and the metal electrodes on the two sides through common processes, so that the vertical cavity surface emitting laser is formed. The direction of the electric injection is perpendicular to the direction of the laser emission, and the influence of the current spreading layer of the ultraviolet band VCSEL on the light field absorption can be avoided. The application is favorable for reducing the damage to the device, improving the yield and the device performance, well utilizing the high-quality material area grown through the lateral epitaxial technology, improving the crystal quality, improving the light emitting efficiency and the service life, and the electric field direction is the non-polarized direction of the material, so that the quantum confinement Stark effect can be effectively reduced, and the reduction of the quantum efficiency and the wavelength drift of the device under a large voltage can be inhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor lasers, and particularly relates to a vertical-cavity surface-emitting semiconductor laser (VCSEL) based on a lateral epitaxial technology and a preparation method thereof. BACKGROUND

[0002] The configuration of a vertical-cavity surface-emitting laser (VCSEL) was first proposed by Professor KENICHI IGA of Tokyo Institute of Technology in 1977. Compared with a traditional edge-emitting laser, a VCSEL has excellent characteristics such as a circular light spot, a low threshold, single-longitudinal-mode output, and easy integration of a two-dimensional array, and has been widely applied to the fields of optical communication and consumer electronics.

[0003] Since the resonant cavity direction of a VCSEL is parallel to the epitaxial direction, the gain medium length is short. Therefore, to achieve lasing, the reflectivity of the upper and lower sides needs to be above 90%, and a distributed Bragg reflector (DBR) is generally used to achieve such high reflectivity. In the long-wave band, the materials used by a VCSEL are mainly gallium arsenide (GaAs) and indium phosphide (InP) systems. For the GaAs system, AlAs / GaAs can be used as high and low refractive index materials at the bottom, and the lattice matching of the two materials is basically matched, and the electrical conductivity and thermal conductivity are very good, which is very suitable for the production of electrically injected VCSEL devices, so the development is very rapid.

[0004] However, in the short-wave band, semiconductor materials with a wider band gap are needed as the gain medium. The VCSELs in the blue-green and ultraviolet bands currently use gallium nitride (GaN) materials, which have many different characteristics compared to the GaAs material system, and also bring a series of technical difficulties.

[0005] 1. Since the GaN system lacks two materials with a large difference in refractive index and a small lattice mismatch, the preparation process of the lower DBR with high reflectivity is complex, and the DBR order or substrate transfer technology needs to be improved, which will result in poor crystal quality or damage to the structure.

[0006] a) The substrate transfer process is often used in the blue-green band. Generally, the GaN epitaxial wafer is first bonded to a bonding substrate, and then the original epitaxial substrate is peeled off by laser peeling. The lower surface DBR coated with a dielectric film system is exposed after thinning by chemical mechanical polishing (CMP). This process is complex, and the two steps of laser peeling and CMP are prone to mechanical damage to the GaN epitaxial film, and it is also difficult to control the cavity length of the vertical cavity.

[0007] b) The UV band uses AlGaN / GaN material. Because of the brittleness of the material, the substrate cannot be transferred by laser ablation, so the DBR is usually formed by epitaxial growth of multiple pairs of nitride. However, a high reflectivity requires many pairs of DBR, which is difficult to grow, and the reflectivity and bandwidth are far less than those of the dielectric film DBR, which limits the performance of the device.

[0008] 2. Because the carrier concentration and mobility of P-type GaN are small, the sheet resistance of P-type GaN is large. A transparent current spreading layer is needed when preparing the P electrode. This material is usually indium tin oxide (ITO). However, the absorption of light by ITO cannot be ignored, and the absorption is more obvious in the UV band. Therefore, ITO cannot be used as a current spreading layer for UV VCSEL, which brings difficulties to the electrical injection of UV VCSEL. The limitation of the current injection method also limits the size of the device, making it difficult to increase the light emitting area and causing a sharp decrease in the light emitting power, which brings great difficulties to the application of the device. This is also an important reason why GaN-based VCSEL lasers have not been widely used.

[0009] 3. Because the electromagnetic field intensity distribution in the vertical cavity is not uniform, the field intensity is maximum at the antinode and minimum at the node. Therefore, the positions of the layers of the device need to be carefully designed: the ITO layer is usually placed at the node of the standing wave field in the vertical cavity to reduce the loss caused by ITO. The InGaN quantum well as the gain medium needs to be placed at the antinode to achieve maximum gain. This requires strict control of the thickness of the device structure.

[0010] To overcome the above technical difficulties of short-wavelength VCSEL, two aspects need to be addressed: one is to find a way to cleverly make the lower DBR, i.e., to pre-locate the DBR before growing the laser structure, to avoid the stripping and transfer process steps and improve the yield; the other is to change the current injection method, separate the current injection direction from the light emission direction, avoid the case where the current injection electrode produces a large light absorption when the injection direction and the light emission direction are the same, and also eliminate the limitation of the light emitting area by the electrode, thereby improving the light emitting power of the VCSEL. As we know, the dielectric film material used to make DBR has a large lattice constant difference from the substrate of the laser, so it is impossible to directly epitaxially grow high-quality laser material on it. Therefore, lateral epitaxial technology can solve this problem and achieve high-quality epitaxial growth and pre-located high-quality DBR. However, the traditional method of using lateral epitaxial technology to prepare VCSEL cannot solve the problem of serious light absorption caused by the coincidence of the current injection direction and the light emission direction, so a new VCSEL structure needs to be designed to solve this problem, which is the core technology of the present application. SUMMARY

[0011] To solve the above technical difficulties, the application provides a vertical cavity surface emitting semiconductor laser based on lateral epitaxial technology and a manufacturing method thereof.

[0012] The technical scheme adopted by the application is as follows:

[0013] A vertical cavity surface emitting semiconductor laser based on lateral epitaxial technology comprises, from bottom to top, a substrate, a lower DBR, a laser structure grown by lateral epitaxy, and an upper DBR; N and P electrodes are arranged on the two sides of the laser structure grown by lateral epitaxy; the current injection direction of the vertical cavity surface emitting semiconductor laser is parallel to the substrate, and the current injection direction is perpendicular to the light emission direction.

[0014] Further, the laser structure grown by lateral epitaxy comprises, in sequence, an N-type semiconductor layer, an N-side light confining layer, an N-side waveguide layer, a quantum well, a P-side waveguide layer, an electron blocking layer, a P-side light confining layer, and a P contact layer.

[0015] Further, the N-type semiconductor layer is a III-V compound semiconductor material or a II-VI compound semiconductor material.

[0016] A manufacturing method of a vertical cavity surface emitting semiconductor laser based on lateral epitaxial technology comprises the following steps:

[0017] 1) preparing a lower DBR on a substrate;

[0018] 2) windowing the lower DBR, and preparing a laser structure by lateral epitaxial technology at the window;

[0019] 3) preparing an upper DBR and N and P electrodes on the two sides of the laser structure prepared by lateral epitaxial technology, to form a vertical cavity surface emitting semiconductor laser.

[0020] Further, the substrate in step 1) is a single-layer mask substrate or a laminated mask substrate; the laminated mask substrate comprises, from bottom to top, a substrate layer, a lower mask, an intermediate layer, and an upper mask, wherein the windows of the lower mask and the upper mask are staggered by a certain distance; the intermediate layer is the lower DBR.

[0021] Further, the substrate in step 1) is a laminated mask substrate, and the lower DBR is formed by the following steps:

[0022] a) preparing a Si3N4 mask on the substrate layer, i.e., a lower mask;

[0023] b) photoetching a window pattern on the Si3N4 mask, removing Si3N4 at the window position by dry etching, exposing the substrate, and then plating a DBR film system;

[0024] c) plating a layer of Si3N4 on the DBR film system, which is the upper mask;

[0025] d) photoetching a window pattern on the upper mask, which is offset from the window of the lower mask by a certain distance in the horizontal plane;

[0026] e) removing Si3N4 at the window position of the upper mask by dry etching, and then etching the intermediate DBR until the window of the lower mask is completely exposed, stopping the etching, thereby completing the pre-setting of the lower DBR.

[0027] Further, the window of the stacked mask substrate is in a variety of patterns such as a strip or a circular hole, and a hexagonal ring VCSEL laser is prepared using the stacked mask substrate with the circular hole window.

[0028] Further, the step 2) of preparing the laser structure by using the lateral epitaxial technology comprises:

[0029] 2.1) growing III-V compound semiconductor material or II-VI compound semiconductor material by using a vertical growth mode;

[0030] 2.2) changing the epitaxial growth conditions, and growing N-type III-V compound semiconductor material or II-VI compound semiconductor material by using a lateral growth mode;

[0031] 2.3) continuing to epitaxially grow an N-side optical confinement layer, an N-side waveguide layer, a quantum well, a P-side waveguide layer, an electron blocking layer, a P-side optical confinement layer, and a P-contact layer, to obtain a lateral epitaxial laser material core-shell structure.

[0032] Further, the step 3) comprises:

[0033] 3.1) performing dry etching on the lateral epitaxial laser material core-shell structure to expose the internal N-type III-V compound semiconductor material or II-VI compound semiconductor material;

[0034] 3.2) preparing an upper DBR on the surface of the material after the dry etching;

[0035] 3.3) performing photoetching on the upper DBR, and removing the upper DBR above the N-type III-V compound semiconductor material or II-VI compound semiconductor material by dry etching;

[0036] 3.4) performing photoetching, and preparing a P electrode by using a vapor plating or sputtering method;

[0037] 3.5) Photolithography is performed and N electrode is prepared by evaporation or sputtering.

[0038] Compared with the traditional VCSEL structure, the present application has the following advantages:

[0039] 1. The lateral epitaxial technique can grow III-V group light emitting semiconductor materials with super-high crystal quality, especially using a stacked mask substrate to grow, which can reduce the dislocation density of GaN material to 10 4 / cm 2 The following is higher than the crystal quality obtained by homo-substrate epitaxial technique, which is very suitable for making lasers. The low dislocation density can significantly reduce non-radiative recombination and improve light emitting efficiency.

[0040] 2. The high-quality DBR is pre-set without introducing additional stress. For example, the refractive index is modulated by different Al component concentrations of GaN / AlGaN, which will inevitably introduce additional stress, and because the refractive index difference is small, a large number of DBRs are needed to achieve high reflectivity and large bandwidth. The oxide optical medium film pre-set by a special evaporation medium film device has good optical performance and does not introduce stress. At the same time, it does not need to use traditional bonding and stripping, the process is simpler, the mechanical damage to the device is smaller, avoids the high failure rate and device performance damage caused by the material stripping process, and is very beneficial to planar array integration.

[0041] 3. The current injection direction is perpendicular to the light emission direction, so there is no need to worry about the large absorption of the laser by the electrode injecting current, so the light emitting area is no longer limited by the injection electrode, and the light emitting area can be greatly increased, which is particularly obvious in ultraviolet band devices. Moreover, the gain medium (quantum well) in the light emission direction is thick, with several microns of gain medium, while the gain medium in the light emission direction of the traditional VCSEL is only tens of nanometers thick, so the new structure has much higher laser gain coefficient than the traditional VCSEL, which is beneficial to improve the light emitting power and light emitting efficiency of the VCSEL. The light emitting power of the traditional VCSEL is only several milliwatts, while the light emitting power of the new structure VCSEL can reach tens of milliwatts or even higher.

[0042] 4. The cavity length of the vertical cavity can be accurately controlled by the growth rate of lateral epitaxial growth and RIE etching.

[0043] 5. The crystal plane of InGaN / GaN quantum well is non-polar a plane or m plane, which can effectively reduce the separation of hole and electron wave functions in space caused by quantum confinement Stark effect (QCSE) under high voltage, improve the radiation recombination rate, and thus improve the internal quantum efficiency of the device, and also effectively suppress the wavelength drift caused by band tilt. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1Figure 1 is a schematic diagram of the cross-section of a vertical cavity surface emitting semiconductor laser based on lateral epitaxy. Wherein: 101. N-type GaN; 102. N-side optical confinement layer; 103. N-side waveguide layer; 104. quantum well (active region); 105. P-side waveguide layer; 106. electron blocking layer; 107. P-side optical confinement layer; 108. P-contact layer; 109. substrate; 110. lower DBR; 111. P-side metal electrode; 112. upper DBR; 113. light emission direction; 114. N-side metal electrode.

[0045] Figure 2 Figure 2 is a schematic diagram of the lateral epitaxy step of a simple substrate structure.

[0046] Figure 3 Figure 3 is a schematic diagram of the preparation process of the upper DBR and N, P electrodes.

[0047] Figure 4 Figure 4 is a schematic diagram of a strip-shaped stacked mask substrate. Wherein: 401. substrate; 402. lower layer mask of the stacked mask substrate; 403. middle layer of the stacked mask substrate, which is also the pre-set VCSEL bottom DBR; 404. upper layer mask of the stacked mask substrate.

[0048] Figure 5 Figure 5 is a schematic diagram of the lateral epitaxy growth of the laser Coreshell material structure on the strip-shaped stacked mask substrate. Wherein: 501. GaN grown in the curved channel, which can annihilate and filter dislocations; 502. lateral epitaxy of the laser material structure.

[0049] Figure 6 Figure 6 is a schematic diagram of the preparation of the completed laser structure on the strip-shaped stacked mask substrate. Wherein: 601. P electrode; 602. N electrode; 603. light emitting surface.

[0050] Figure 7 Figure 7 is a schematic diagram of a hexagonal prism obtained by point-like central lateral epitaxy. Wherein: 701. hexagonal prism Coreshell structure of the laser material structure required by epitaxy; 702. pre-set bottom DBR; 703. sapphire or Si, etc. substrate that can epitaxially grow GaN.

[0051] Figure 8 Figure 8 is a schematic diagram of the material structure of the hexagonal prism center section. Wherein: 801. GaN grown from the circular point-like stacked mask window along the curved channel; 802. lateral epitaxy of the laser hexagonal prism Coreshell structure; 803. pre-set bottom DBR.

[0052] Figure 9 Figure 9 is a hexagonal prism VCSEL laser with electrodes. Wherein: 901. N-type metal electrode; 902. top DBR, light emitting area; 903. P-type metal electrode. DETAILED DESCRIPTION

[0053] The application will be further described in detail by specific examples and drawings.

[0054] The application proposes a new structure of vertical cavity surface emitting semiconductor laser based on lateral epitaxial technology, and its manufacturing method. The structure and manufacturing method can be applied to various semiconductor laser materials. For convenience, the application is described below by taking the light emitting material GaN as an example, and its structure diagram is shown in Figure 1 .

[0055] As shown in Figure 1 , from bottom to top, there are a sapphire substrate 109 (or other substrate that can epitaxially grow GaN), a lower DBR film system 110, and a GaN-based laser structure 101-108 grown by lateral epitaxy, including N-type GaN, InGaN / GaN quantum well as an active region, P-type GaN, etc. The uppermost is an upper DBR film system 112, which can be SiO2 / HfO2 or SiO2 / TiO2 or other materials. The laterally distributed 114 is Ti / Al / Ni / Au (or other metal film system) N metal electrode, and 111 is Ni / Au (or other metal film system) P metal electrode.

[0056] The new structure proposed by the application is implemented in two parts. The core goal of the first part is to realize the pre-set DBR and lateral epitaxy, and the core goal of the second part is to realize the top DBR and the preparation of N and P electrodes. Each part contains several specific implementation steps.

[0057] Example 1:

[0058] The first part is the implementation steps of the pre-set DBR and lateral epitaxy:

[0059] As we know, there are various ways to implement lateral epitaxial technology. One of the simpler ways is to pre-deposit a layer of mask material on the epitaxial substrate, and then remove part of the mask material by etching or etching, so that part of the substrate surface is exposed. The epitaxial material grows upwards from the exposed substrate part, and then the material grows laterally by changing the growth conditions, which is lateral epitaxy. There is also a complex stacked substrate epitaxial technology, which is relatively complex to prepare the substrate, but the quality of the grown crystal material is higher. The two kinds of lateral epitaxial technology on the substrate will be introduced respectively.

[0060] The following will introduce the specific content of the present application by taking the growth of GaN material on a sapphire substrate as an example, but it should be noted that the substrate is not limited to sapphire, and can be other substrates suitable for epitaxial growth of III-V semiconductors (such as Si, SiC, etc.), and the material to be grown is not limited to GaN, and can be other III-V semiconductor materials (InN, AlN, InGaN, AlGaN, GaAs, InP, etc.).

[0061] As shown in Figure 2 , the lateral epitaxy of the simple substrate structure includes the following steps:

[0062] 201. Prepare a sapphire substrate.

[0063] 202. On the sapphire substrate, first coat a high-quality DBR. The material type and structure of the DBR need to be designed according to the target wavelength and bandwidth, and professional simulation software can complete a relatively accurate design. Then, through a professional optical medium film coating device (electron beam evaporation or reactive magnetron sputtering, etc.), the designed DBR film system is coated to achieve the predetermined high reflectivity.

[0064] 203. Next, perform photolithography and design a photolithography pattern according to the area of the sapphire substrate that needs to be exposed.

[0065] 204. After exposing and developing the desired pattern, use ICP or RIE to etch the desired pattern and expose the sapphire substrate.

[0066] 205. Perform glue removal and cleaning.

[0067] 206. After glue removal and cleaning, use MOCVD equipment to epitaxially grow GaN. First, perform vertical growth mode growth (i.e., a growth mode in which the vertical growth rate is greater than the lateral growth rate).

[0068] 207. Change the epitaxial growth conditions to a lateral growth mode (i.e., a growth mode in which the lateral growth rate is greater than the vertical growth rate), start lateral epitaxy, and first grow a N-type GaN layer laterally.

[0069] 208. Then continue to epitaxially grow the entire required structure of the laser, from the inside out, including the N-side light confinement layer, the N-side waveguide layer, the quantum well (active region), the P-side waveguide layer, the electron blocking layer, the P-side light confinement layer, and the P-contact layer, etc.

[0070] After completing the epitaxial growth of the required material structure of the laser, the next step is to start preparing the top DBR and N and P electrodes.

[0071] Second part, top DBR and N, P electrode manufacturing steps

[0072] As shown in Figure 3 , the top DBR and N, P electrode fabrication steps specifically include: 301. Lateral epitaxial good laser material Coreshell structure; 302. Dry etching, exposing N-type GaN inside the Coreshell structure; 303. Plating top DBR; 304. Photolithography, exposing the part that needs to be etched; 305. Dry etching to remove DBR above N-type GaN, exposing N-type GaN, and removing the adhesive; 306. Photolithography, exposing P-type GaN, waiting for P electrode plating; 307. Using evaporation or sputtering method, plating metal electrodes such as Ni / Au suitable for P-type GaN contact; 308. Removing the adhesive, peeling off the excess metal, leaving the P electrode; 309. Photolithography, exposing N-type GaN, preparing for N electrode plating; 310. Using evaporation or sputtering method, plating metal electrodes such as Ti / Al / Ni / Au suitable for N-type GaN contact; 311. Removing the adhesive, peeling off the excess metal, leaving the N electrode.

[0073] The lateral epitaxial laser material is a Coreshell structure as shown in Figure 2 208, which contains all the material structures required by the laser (the schematic diagram only roughly shows the material structure, and the actual laser material structure parameters will be more complex). As shown in Figure 3 , on the basis of lateral epitaxial Coreshell structure, first use dry etching method to etch downward directly until the N-type GaN inside the Coreshell structure is exposed, as shown in Figure 3 302. Then use evaporation or reactive magnetron sputtering method to plate top DBR according to the designed parameters, generally the reflectivity of top DBR is slightly lower than that of bottom DBR. Then perform photolithography to expose the position above N-type GaN that needs to be etched. Then use RIE dry etching to remove DBR above N-type GaN, exposing N-type GaN, and removing the adhesive. Then use negative adhesive photolithography to expose P-type GaN, and use evaporation or sputtering method to plate metal electrodes such as Ni / Au suitable for P-type GaN contact. Use organic solvents such as acetone to remove the adhesive and peel off the excess metal, leaving the P electrode. At this time, P electrode annealing can be performed to make the P electrode contact well. Then perform negative adhesive photolithography again to expose N-type GaN, and use evaporation or sputtering method to plate metal electrodes such as Ti / Al / Ni / Au suitable for N-type GaN contact. Remove the adhesive and peel off the excess metal, leaving the N electrode. At this point, the basic fabrication process of this structure laser is completed, and subsequent packaging and testing can be performed.

[0074] Example 2:

[0075] In practical implementation, various schemes can be used to realize the core structure of this design. In this embodiment, a multilayer mask substrate technique is used for lateral epitaxy to achieve higher crystal quality than ordinary lateral epitaxy techniques. Multilayer mask technology is a novel lateral epitaxy technique that has emerged in recent years. Its core principle is to use a three-dimensional mask substrate to orient the material during growth within curved channels, thereby achieving the purpose of merging and filtering dislocations, which greatly improves the crystal quality of the portion emerging from the window during lateral epitaxy, resulting in an overall improvement in the material's performance. This embodiment uses a strip-shaped multilayer substrate lateral epitaxy technique to illustrate the specific implementation steps of the present invention.

[0076] The fabrication of multilayer mask substrates is slightly more complex than that of ordinary lateral epitaxy (ELOG) substrates. Firstly, GaN must be epitaxially grown on a substrate (i.e.,...) Figure 4 In the 401 substrate (such as sapphire, Si, or SiC), a high-density Si3N4 layer is deposited. Low-pressure chemical vapor deposition (LPCVD) is typically used to grow a Si3N4 mask several tens of nanometers thick, which serves as the lower mask (i.e., the substrate itself). Figure 4 (402 in the text). Generally, GaN does not nucleate and grow on highly dense Si3N4 films, so it can be used as a mask. Furthermore, dense Si3N4 exhibits a slow etching rate in HF acid solution, which is beneficial for the subsequent fabrication of suspended structures. Then, the designed window pattern is photolithographically etched onto the underlying Si3N4 mask. The Si3N4 at the window locations is removed using RIE dry etching, exposing the substrate. These locations will be the starting points for GaN material nucleation and growth. Then, the designed DBR (i.e.,...) is deposited. Figure 4 In the 403 layer (referring to a specific type of substrate), multiple SiO2 / TiO2 DBR films are typically grown using electron beam evaporation or reactive magnetron sputtering. This is because SiO2 / TiO2 is easily corroded by HF acid solution, which is beneficial for the subsequent fabrication of suspended structures in the multilayer mask substrate. A high-density Si3N4 layer is then deposited on top of the SiO2 / TiO2 film using LPCVD, forming the upper mask (i.e., the layer containing the SiO2 / TiO2 film). Figure 4 The thickness of the 404 layer (as described in the image) is designed based on the laser's emission wavelength and its refractive index. The final thickness is designed to be half the wavelength optical path to increase reflectivity. A window pattern is photolithographically etched onto the upper mask, offset horizontally from the window on the lower mask. Then, dry etching using RIE removes the Si3N4 at the window location on the upper mask. Finally, BOE solution is used to etch the DBR in the middle. Because the etching rate of Si3N4 is slow while that of DBR is fast, a suspended structure can be formed during etching. Figure 4As shown, etching stops when the window on the lower mask is completely exposed. This completes the fabrication of the stacked mask substrate and the pre-setting of the DBR. Afterwards, MOCVD can be used to epitaxially grow GaN (i.e., GaN) on this stacked mask substrate. Figure 5 (referring to 501 in the original text). By adjusting the epitaxial growth parameters, GaN can be grown starting from the window of the bottom mask. In the curved channels of the stacked mask substrate, dislocations are merged and annihilated. When it grows out from the upper window, it is already a high-quality GaN material. Further changing the growth conditions, slowing down the longitudinal growth rate and accelerating the lateral growth rate, initiates lateral epitaxy. When all the structures required for the laser are laterally epitaxially grown, a structure like... Figure 5 The Coreshell structure shown in Figure 502 can be used for subsequent processes.

[0077] After completing the epitaxial growth of the material structure, the morphological structure of the laser needs to be fabricated, mainly including the fabrication of the top DBR and the N and P electrodes. The main fabrication steps are as follows... Figure 3 As shown. Based on the lateral epitaxial coreshell structure, dry etching is first used to directly etch downwards until the N-type GaN inside the coreshell structure is exposed. Then, the top surface DBR is deposited according to the designed parameters using methods such as vapor deposition or reactive magnetron sputtering. Next, photolithography is performed to expose the areas above the N-type GaN that need to be etched. Then, RIE dry etching is used to remove the DBR above the N-type GaN, exposing the N-type GaN, and the resist is removed. Then, negative resist photolithography is used to expose the P-type GaN, and Ni / Au or other metal electrodes suitable for P-type GaN contact are deposited using vapor deposition or sputtering. The resist is removed using an organic solvent such as acetone, and excess metal is stripped away, leaving the P electrode (i.e., Figure 6 (601 in the text). At this point, P-electrode annealing can be performed to ensure good P-electrode contact. Then, negative photolithography is performed again to expose the N-type GaN. Suitable metal electrodes such as Ti / Al / Ni / Au for N-type GaN contact are deposited using evaporation or sputtering. The resist is then removed, excess metal is stripped off, leaving the N-electrode (i.e., 601 in the text). Figure 6 (602 in the text). This completes the basic fabrication process of the laser structure, and the final structure is as follows. Figure 6 As shown, subsequent steps include packaging and testing.

[0078] For VCSEL lasers fabricated on strip-shaped multilayer substrates, the structure is as follows: Figure 6 As shown, it has some outstanding advantages:

[0079] 1. The light emitting surface can extend in the direction of the bar, so the total light emitting area will be greatly increased, so that the total power can be much larger than the traditional VCSEL laser. The length of the active region in the light emitting direction is on the order of several microns, much larger than the gain medium thickness of several nanometers of traditional VCSEL, so higher gain can be obtained, thereby reducing the lasing threshold.

[0080] 2. The active region, waveguide layer, light confinement layer and other important structures are located in the laterally epitaxial high crystal quality area, which can effectively reduce non-radiative recombination and light absorption, thereby improving the light emitting efficiency. Since the active region is grown on a non-polar surface, the direction of the applied electric field is perpendicular to the polarization direction of the material, so the quantum Stark limitation effect can be effectively reduced, thereby improving the device performance.

[0081] Embodiment 3:

[0082] In this embodiment, the implementation of other shape VCSEL lasers will be shown, such as hexagonal ring VCSEL laser. Since the crystal structure of GaN material has six-fold symmetry, if lateral epitaxy is performed with a point-like center, a hexagonal prism or hexagonal pyramid will be grown. By controlling the growth conditions of lateral epitaxy, a relatively regular hexagonal prism can be obtained, as shown in Figure 7 , where 701 is a hexagonal prism Coreshell structure of the material structure required for epitaxial good laser, 702 is a pre-embedded bottom DBR, and 703 is a substrate such as sapphire or Si that can epitaxially grow GaN.

[0083] According to the design wavelength of the laser, the size of the hexagonal prism can be optimized and designed, and then the growth thickness of each layer can be accurately controlled through epitaxy technology. The internal material structure is as shown in Figure 8 , a cross-sectional view is taken through the center, and the structure of the stacked substrate and the lateral epitaxial structure can be seen, where 801 is GaN grown from a circular point-like stacked mask window along a curved channel, 802 is a hexagonal prism Coreshell structure of the laser, and 803 is a pre-embedded bottom DBR. Unlike the stacked substrate of the bar, the bottom window of the stacked substrate is a circular hole, and the upper window is also a circular hole, which are offset by a certain distance in the plane direction, so as to form a curved channel, which can also achieve the functions of merging and filtering dislocations. The middle layer of the stacked mask is a pre-embedded bottom DBR. By controlling the size of the hexagonal prism, the laser core structure is opposite to the complete DBR below. After the GaN of the stacked mask substrate is grown, lateral epitaxy is performed, and since it is a point-like center, it will grow in all directions. According to the crystal symmetry, a hexagonal prism is finally formed.

[0084] After the epitaxial structure is completed, the second stage of the process manufacturing process is performed, including the preparation of the upper DBR and N and P electrodes. The specific manufacturing process is as shown in Figure 3The basic structure is shown in the figure. First, etching is performed to remove the planar structure on the top of the core-shell structure, exposing the N-type GaN inside the core. Then, a special device is used to plate a top DBR, followed by photolithography to expose the position that needs to be etched above the N-type GaN. Then, dry etching is used to remove the DBR above the N-type GaN, exposing the N-type GaN and removing the photoresist. Then, negative photoresist lithography is used to expose the P-type GaN, and evaporation or sputtering method is used to plate metal electrodes such as Ni / Au suitable for P-type GaN contact. Use organic solvents such as acetone to remove the photoresist and peel off the excess metal, leaving the P electrode. At this time, P electrode annealing can be performed to ensure good P electrode contact. Then, negative photoresist lithography is performed again to expose the N-type GaN, and evaporation or sputtering method is used to plate metal electrodes such as Ti / Al / Ni / Au suitable for N-type GaN contact. Remove the photoresist and peel off the excess metal to leave the N electrode. At this point, the basic fabrication process of the structure laser is completed, and the completed laser structure is shown in the figure Figure 9 where 901 is the N-type metal electrode, 902 is the top DBR, i.e. the light emitting area, and 903 is the P-type metal electrode. Subsequent packaging and testing can be performed.

[0085] Compared with Examples 1 and 2, in addition to the advantages of long strip shape, the hexagonal prism VCSEL laser also has the advantage that the laser far-field spot is close to a circle, and can be designed and adjusted according to the size, so that a VCSEL with a circular spot and a ring-shaped spot can be prepared. Since the length of the light emitting area is about the circumference of the prism, the size adjustment can also adjust the light emitting power.

[0086] In general, the change of the substrate used for lateral epitaxy, the change of the DBR material type, and the change of the lateral epitaxy shape do not affect the core structure of the present application. The epitaxial material is not limited to GaN material, but can also be other semiconductor laser materials that can be grown by epitaxy, such as III-V compound semiconductors AlGaN, InGaN, AlN, InN, GaAs, InP, etc., and also includes II-VI compound semiconductors.

[0087] The core of the new structure is to solve the problem of pre-setting the lower DBR by lateral epitaxial technology. The traditional VCSEL laser needs to separate the laser structure from the substrate and then bond the DBR on the back to achieve high reflectivity. The laser separation process has a great damage to the device, resulting in a low yield. The present application first pre-sets the DBR, then opens a window on the DBR, and then uses lateral epitaxial technology to grow the functional area of the laser on the top of the DBR to complete the preparation of the lower DBR of the VCSEL, and then prepare the upper DBR and the metal electrodes on both sides through the common process, thereby forming a vertical cavity surface laser. The direction of the electric injection is parallel to the substrate, the carriers are combined in the active region, the photons are formed between the upper and lower DBRs, the resonance is formed by the back and forth reflection, and the laser is emitted in the direction perpendicular to the substrate after meeting the lasing condition. The direction of the electric injection is perpendicular to the direction of the laser emission, which can avoid the influence of the current spreading layer of the ultraviolet band VCSEL on the light field absorption. Since the preparation of the lower DBR does not need the bonding and laser separation process of the traditional GaN-based VCSEL, it is beneficial to reduce the damage to the device, improve the yield and the performance of the device. Moreover, the structure makes good use of the high-quality material area grown by the lateral epitaxial technology, improves the crystal quality, and thus improves the light-emitting efficiency and the life. And the electric field direction is the non-polar direction of the material, which can effectively reduce the quantum confinement Stark effect (QCSE), thereby suppressing the reduction of quantum efficiency and wavelength drift of the device under high voltage.

[0088] The specific embodiments of the present application disclosed above are intended to help understand the content of the present application and to implement the same, and those skilled in the art can understand that various replacements, changes and modifications are possible without departing from the spirit and scope of the present application. The present application should not be limited to the content disclosed in the embodiments of the present application, and the protection scope of the present application is defined by the scope of the claims.

Claims

1. A vertical cavity surface emitting semiconductor laser based on lateral epitaxy technology, characterized in that From bottom to top, the vertical cavity surface emitting semiconductor laser comprises a substrate, a lower DBR, a laterally epitaxially grown laser structure, and an upper DBR; the laterally epitaxially grown laser structure is provided with an N electrode and a P electrode on both sides thereof; the current injection direction of the vertical cavity surface emitting semiconductor laser is parallel to the substrate, and the current injection direction is perpendicular to the light emission direction; the laterally epitaxially grown laser structure comprises, in sequence, an N-type semiconductor layer, an N-side optical confinement layer, an N-side waveguide layer, a quantum well, a P-side waveguide layer, an electron blocking layer, a P-side optical confinement layer, and a P contact layer; the normal of the N-side optical confinement layer, the N-side waveguide layer, the quantum well, the P-side waveguide layer, the electron blocking layer, the P-side optical confinement layer, and the P contact layer is perpendicular to the normal of the substrate.

2. The lateral epitaxial side technology based vertical cavity surface emitting semiconductor laser of claim 1, wherein, The N-type semiconductor layer is a III-V compound semiconductor material or a II-VI compound semiconductor material.

3. A method of manufacturing a vertical cavity surface emitting semiconductor laser based on lateral epitaxial technology according to claim 1 or 2, characterized in that The method comprises the following steps: 1) preparing a lower DBR on a substrate; 2) windowing the lower DBR, and preparing a laser structure at the window by using a lateral epitaxial technology; 3) preparing an upper DBR and an N electrode and a P electrode on both sides of the laser structure prepared by using the lateral epitaxial technology, to form a vertical cavity surface emitting semiconductor laser; In step 2), the laser structure is prepared by using the lateral epitaxial technology, which comprises the following steps: 2.1) growing a III-V compound semiconductor material or a II-VI compound semiconductor material by using a vertical growth mode; 2.2) changing the epitaxial growth conditions, and growing an N-type III-V compound semiconductor material or a II-VI compound semiconductor material by using a lateral growth mode; 2.3) continuing to epitaxially grow an N-side optical confinement layer, an N-side waveguide layer, a quantum well, a P-side waveguide layer, an electron blocking layer, a P-side optical confinement layer, and a P contact layer, to obtain a laterally epitaxially grown laser material core-shell structure.

4. The method of claim 3, wherein, In step 1), the substrate is a single-layer mask substrate or a laminated mask substrate; the laminated mask substrate comprises, in sequence from bottom to top, a substrate layer, a lower mask, an intermediate layer, and an upper mask, wherein the windows of the lower mask and the upper mask are staggered by a certain distance; the intermediate layer is the lower DBR.

5. The method of claim 4, wherein, In step 1), the substrate is a laminated mask substrate, and the lower DBR is prepared by using the following steps: a) preparing a Si3N4 mask on the substrate layer, i.e., the lower mask; b) performing photoetching on the Si3N4 mask to form a window pattern, removing Si3N4 at the window position by dry etching, exposing the substrate, and then plating a DBR film system; c) plating a layer of Si3N4 on the DBR film system, i.e., the upper mask; d) performing photoetching on the upper mask to form a window pattern, wherein the window is staggered by a certain distance from the window of the lower mask in the horizontal plane; e) removing Si3N4 at the window position of the upper mask by dry etching, and then etching the intermediate DBR until the window of the lower mask is completely exposed, to stop etching, thereby completing the preparation of the lower DBR.

6. The method of claim 4, wherein, The window of the laminated mask substrate is in the shape of a strip or a circular hole; a hexagonal ring-shaped VCSEL laser is prepared by using the laminated mask substrate with the circular hole-shaped window.

7. The method of claim 3, wherein, Step 3) comprises: 3.1) dry etching the laser material core-shell structure extending laterally to expose the inner N-type III-V compound semiconductor material or II-VI compound semiconductor material; 3.2) preparing an upper DBR on the surface of the dry etched material; 3.3) performing photolithography on the upper DBR and removing the upper DBR above the N-type III-V compound semiconductor material or II-VI compound semiconductor material by dry etching; 3.4) performing photolithography and preparing a P electrode by evaporation or sputtering; 3.5) performing photolithography and preparing an N electrode by evaporation or sputtering.

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